Disclosed herein are radiation curable phase change ink compositions ideally suited for use in digital lithographic printing devices. In embodiments, the ink includes a polyester transfer additive. The ink vehicle may also contain additional curable components, and may also contain an initiator for curing upon exposure to radiation.
Ink-based digital printing uses a variable data lithography printing system, or digital offset printing system, or a digital advanced lithographic imaging system. A “variable data lithography system” is a system that is configured for lithographic printing using lithographic inks and based on digital image data, which may be variable from one image to the next. While “Variable data lithography printing,” or “digital ink-based printing,” or “digital offset printing,” or digital advanced lithography imaging is printing of variable image data for producing images on a substrate that are changeable with each subsequent rendering of an image on the substrate in an image forming process.
For example, a digital offset printing process may include transferring radiation-curable ink onto a portion of a fluorosilicone-containing imaging member or printing plate that has been selectively coated with a dampening fluid layer according to variable image data. Regions of the dampening fluid are removed by exposure to a focused radiation source (e.g., a laser light source) to form pockets. A temporary pattern in the dampening fluid is thereby formed over the printing plate. Ink applied thereover is retained in the pockets formed by the removal of the dampening fluid. The inked surface is then brought into contact with a substrate and the ink transfers from the pockets in the dampening fluid layer to the substrate. The dampening fluid may then be removed, a new uniform layer of dampening fluid applied to the printing plate, and the process repeated. The ink is then transferred from the printing plate to a substrate such as paper, plastic, or metal on which an image is being printed and cured. The same portion of the imaging plate may be optionally cleaned depending on ink type and used to make a succeeding image that is different than the preceding image, based on the variable image data.
Digital offset printing inks differ from conventional inks because they must meet demanding rheological requirements imposed by the lithographic printing process while being compatible with system component materials and meeting the functional requirements of sub-system components, including wetting and transfer. Print process studies have demonstrated that higher viscosity is preferred for ink transfer to digital lithography imaging blanket from the inker unit via a roll and yet even higher viscosity is needed to improve transfer to a print substrate. Therefore, there remains a need for digital advanced lithography imaging inks to have increased viscosity latitude to enable excellent ink transfer from the ink loader system at both about 60° C. and excellent ink delivery from the anilox roller to the fluorosilicone blanket at temperatures as low as about 20° C.